As an example of using biomass energy, an attempt has been made for yielding ethanol by decomposing a cellulose or hemicellulose, which is a main component of plants, to produce a saccharified solution and then fermenting the resultant saccharide into alcohol. In the attempt, it has been planned to use the resultant ethanol for fuel and make a partial blend of ethanol mainly into a fuel for automobiles, or use a fuel alternative for gasoline.
In recent years, the following technique has also been industrially performed: a technique of decomposing a cellulose or hemicellulose, supplying the resultant saccharified solution to lactic acid fermentation to produce L-lactic acid, and then polymerizing this acid to produce polylactic acid, which is a bio-base polymer species. Attention has been paid to polylactic acid as a biodegradable plastic material.
Plants include, as main components thereof, any cellulose (polymer made from glucose, which is a C6 monosaccharide having 6 carbon atoms), any hemicellulose (polymer made from a C6 monosaccharide, and a C5 monosaccharide having 5 carbon atoms), lignin, and starch. Ethanol is produced by a fermentation effect of microorganisms, such as yeast, using as a raw material a C5 monosaccharide, a C6 monosaccharide, an oligosaccharide which is a complex of these monosaccharides, or some other saccharide as a raw material.
In order to decompose a cellulose-type biomass such as a cellulose or a hemicellulose into a saccharide, the following three methods are to be industrially used: a method 1) of hydrolyzing the biomass by the oxidizing-power of a strong acid such as sulfuric acid, a method 2) of decomposing the biomass by an enzyme, and a method 3) of using the oxidizing power of supercritical water or subcritical water. Out of these methods, the enzyme decomposition method 2) has a drawback of being longer in decomposition period than the other decomposition methods, but has advantages of being low in production-facility costs, and running costs, being capable of attaining a normal-temperature and normal-pressure treatment, and not causing an excessive decomposition of saccharides.
Patent Literature 1 discloses that in the case of transferring a lignocellulose-type biomass subjected to lignin removal or swelling treatment into a reactor for enzyme saccharification reaction through, for example, a vessel for transfer, miscellaneous bacteria are unfavorably incorporated into the lignocellulose-type biomass, for example, at the time of the shift of the lignocellulose-type biomass into the vessel for transfer, and discloses that when the lignocellulose-type biomass, into which the miscellaneous bacteria are incorporated, is caused to react for saccharification through an enzyme, the produced saccharides are consumed with the incorporated miscellaneous bacteria.
In order to solve such problems, Patent Literature 1 discloses a method for treating a lignocellulose-type biomass, this method being a lignocellulose-based-biomass-treating method of pretreating the lignocellulose-type biomass in one reactor, shifting the biomass into different reactors, and saccharifying the biomass with an enzyme to yield a saccharified solution, and being characterized by including a pretreating step of pretreating the lignocellulose-type biomass in the reactor, which is a first reactor, to dissociate lignin from the lignocellulose-type biomass or swell the lignocellulose-type biomass to yield a first treated product, a first saccharifying treatment step of subjecting the first treated product yielded through the first treatment step partially to enzyme saccharification reaction in one of the different rectors, which is a second reactor, to yield a second treated product, a transferring step of transferring the second treated product yielded through the first saccharifying treatment step in the state of bringing this product into no contact with any external air, and a second saccharifying step of subjecting the second treated product transferred through the transferring step to enzyme saccharification reaction in one of the different rectors, which is a third reactor, to yield a saccharified solution.
As a method for hydrolyzing a cellulose in a very short period without requiring shearing, Patent Literature 2 discloses a method for hydrolyzing a lignocellulose biomass, including:
a step A of bringing a lignocellulose raw-material containing a biomass having a dry content and water into contact with at least one portion of a solvent containing water-soluble hydrolysis species, at least some of the water-soluble hydrolysis species being equal to water-soluble hydrolysis species that can be yielded by hydrolysis of the biomass in the raw-material,
a step B of maintaining contact between the raw-material in raw-material flow and the solvent at a temperature ranging from 20 to 200° C. for a period of 5 minutes to 72 hours to produce a hydrolyzed product from the biomass in the raw-material.
As a method capable of increasing the production amount of saccharides made mainly of glucose even when enzyme saccharification reaction is conducted with a small quantity of an enzyme,
Patent Literature 3 discloses a method of decomposing a cellulose and/or a hemicellulose with a cellulose hydrolase to produce saccharides made mainly of glucose,
in which: the cellulose and/or the hemicellulose is/are mixed with an aqueous enzyme solution of the cellulose hydrolase; and subsequently while the mixture is stirred to mix the components with each other to satisfy the following relationship expression: Y≤−0.0125×2+1.195×+23.25 in which Y represents stirring power (W/m3) applied to the mixture of the cellulose and/or hemicellulose, and the aqueous enzyme solution, and X represents the addition ratio (w/v %) of the cellulose and/or the hemicellulose to the aqueous enzyme solution, an enzyme saccharification reaction is conducted for saccharifying the cellulose and/or the hemicellulose with the cellulose hydrolase.